Electric heater



A ril 14, 1964 w; -r. HAGE ETAL I 3,129,314

ELECTRIC HEATER Filed Aug. 1, 1960. 2 Sheets-Sheet l lN-VENTORS William T. Hage 3 By Johanpes H. Ammon Fredergfii Harfwig v ATTORNEY April 14, 1 4 w. r. HAGE ETAL 3,129,314

zusc'raxc HEATER Filed Aug. 1, 1960 2 Sheets-Sheet 2 1A(VENT0R5 WI Ill T. Hage y Johanne Am-mon Frederigd Harrwig ATTORNEY Unitcd States Patent 3,129,314 ELECTRIC HEATER William T. Hage, Alliance, Johannes H. Ammon, Barberton, and Frederick J. Hartwig, Alliance, Ohio,

assignors to The Babcock & Wilcox Company, New

York, N.Y., a corporation of New Jersey Filed Aug. 1, 1960, Ser. No. 46,755 4 Claims. (Cl. 219-19) This invention relates in general to electric heaters and more specifically to high capacity immersion heaters which are capable of operating when submerged in a high pressure vaporizable liquid with a high heat output per unit area of the heater.

Immersion heaters as now known in the art are limited by the comparative low heat output obtained per unit area of the heater, the limiting conditions under which they may be operated, or a combination of these two factors. Usually, when a heater is operated in a fluid at elevated pressures, the rate of heat output must be sacrificed to enable it to withstand the elevated pressure. One reason such heaters are not capable of high heat output per unit area is the fact that the resistance elements within the heater sheath are formed of spaced ire or ribbon components which have less effective surface in the resistance element than is present in the heater element here disclosed. Many of the heaters in use today utilize an insulation material which is soluble in Water, e.g. magnesium oxide. This creates the risk of contaminating the liquid which is being heated, should the covering sheath fail. Thus where the purity of the liquid being heated is of the utmost concern, such a heater is provided with a thicker walled sheath that pressure requirements dictate, thereby reducing the output per heater as well as increasing the cost.

The present invention provides a high capacity immersion resistance heater that has a greatly increased output per unit area of the heater over those heaters now known to the art. This heater has the largest re sistance element surface that is possible within a given volume. Moreover, the element is separated from the covering sheath only by a thin and coherent film of electrical insulation material. This heater design also has the desirable features of being easily and inexpensively fabricated.

Accordingly, the present invention provides an electric heater with an electric resistance element formed of at least two longitudinally contiguous arcuate members connected together at one end to form a longitudinally slotted cylinder, a covering sheath adapted to enclose the resistance element, and a thin and coherent film of dielectric material disposed between the covering sheath and the resistance element. The resistance element, the dielectric material, and the sheath are urged and maintained in intimate contact by the compacting of a finely divided refractory material which is disposed within the slotted cylinder. A terminal member, insulated from the sheath, is connected to each arcuate member to provide a connection to a source of electric power.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described the preferred embodiment of the invention.

Of the drawings:

FIG. 1 is a longitudinal section through the heater of this invention;

FIG. 2 is a transverse section taken along line 22 of FIG. 1;

3,129,314 Patented Apr. 14, 1964 FIG. 3 is an exploded view of the heater of the present invention; and

FIG. 4 is an enlarged view of part of the wall cross section as taken from FIG. 1.

A longitudinal section of the high capacity immersion heater 10 is shown in FIG. 1. The heater 10 is comprised of a heater resistance element 12, a covering sheath 16, and electric terminals 24. The resistance element 12 is a longitudinally elongated hollow member divided longitudinally into two sections 12' and 12" which are connected together at one end by a connecting sleeve 14 which has slots extending partially along its length to mate with the slots 13 between the sections. The slots 13, and the mating slots in the connecting sleeve 14, permit the two sections to be expanded, the purpose of which will be more thoroughly described hereinbelow. At the opposite end of the resistance element 12 from the connecting sleeve 14, electric terminals 24 and 24' are connected to the sections 12' and 12", respectively, to provide connections to a source of electric power. Preferably, the resistance elements 12' and 12" are longitudinally contiguous arcuate members, shown in FIGS. 2 and 3 as two half-cylinders, joined together by the connecting sleeve 14 to form a hollow cylinder with a wall thickness between 0.007 and 0.015 inch and preferably about 0.010 inch. The resistance elements are formed of an electric resistance heating material such as Nichrome metal percent nickel, 20 percent chromium), an iron-nickel alloy, a copper-nickel alloy, or other such alloys as are well known in the art, while the connecting sleeve 14 is formed of a material with low thermal resistivity such as copper or stainless steel.

The resistance element 12 is positioned within the covering sheath 16 and separated therefrom by a thin, dense, and coherent film of dielectric material 22. The covering sheath 16 is closed at one end by closure 18 that is fastened thereto by weld 20. The dielectric material 22 may be a vitreous enamel such as porcelain, a semi-vitreous enamel containing a refractory material, a thin glass coating, or other material as is well known in the art. This may be deposited on the inner surface of the covering sheath 16 or the outer surface of the resistance element 12 to form an electrical insulator therebetween capable of withstanding high operating temperatures, the differential temperatures associated therewith, and the electrical potential applied. The thickness of this dielectric is as thin as practicable and yet able to provide proper electrical insulation.

A compression rod 28, axially aligned within the covering sheath 16, is provided with a threaded end portion 32 which is attached to the sheath closure 18. The opposite end of the compression rod 28 is also threaded, as at 30, and will be more thoroughly described hereinbelow.

After the resistance element 12 is fitted within the covering sheath 16, the annular space 26 between the resistance element and the compression rod 28 is filled with a plurality of refractory pebbles or granules 34 such as silica. An electrically now-conductive compression disk 36, adapted to fit over the compression rod 28 and to close the annular space 26, is fitted over the threaded portion 30 of the compression rod. A nut 38 then forces the compression disk into the space 26 which in turn compresses the refractory granules 34, forcing the resistance member into intimate contact with the dielectric material 22. Other methods of expanding the resistance element 30 against the dielectric material 22 and the covering sheath 16 may be used such as a solid expanding filler in place of the refractory 34, or by mechanically expanding the resistance element.

A specific example of a heater as described above is one in which the cylindrical resistance element is fabri- The completed element is then inserted within a inch' thick steel covering sheath having a vitreous lining 0.005 inch thick. The inner space of the resistance element is then filled with silica pebbles which are compacted to expand the sections of the resistance element against the vitreous lining of the covering sheath. With this heater, as an example, it has been possible to attain a heat output of 194 watts per square inch of external area of the heater.

The present invention provides a high capacity immersion heater which is comparatively easy to fabricate. The present invention is an improvement over that of the prior artbecause of several factors; first, the resistance element is substantially equal to the size of the heater. The use of a heater element comprised of two arcuate members so joined as to form a longitudinally slotted cylinder creates a resistance element with an area nearly equal to that of the entire heater. The second factor is the use of a thin, dense, and coherent layer of a dielectric material between the resistance element and the covering sheath to prevent short circuiting between the two halves of the element or between the element and the exterior of the covering sheath. Further, the fact that this layer is very thin reduces the thermal resistance between the resistance element and the sheath. The third factor contributes to the high capacity in the use of the refractory pebbles within the heating element to force the element into intimate contact with the dielectric material which, in turn, is in intimate contact with the covering sheath. As a result of this forced contact there are no air spaces between the two surfaces which could act as an insulator and thus reduce the output of the heater.

With the immersion heater herein described, we have been able to achieve a high capacity output per unit area of the heater, with a simple, rugged design. As a comparison, present Calrod type heaters have a heat output of approximately 100 watts per square inch of heater outside area. The heater as herein described has achieved a heat output of nearly 200 watts per square inch.

While in accordance with the provisions of the statutes we have illustrated and described herein the best forms and modes of operation of the invention now know to us, those skilled in the art will understand that changes may be made in the forms of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. An electric heater comprising an electric resistance element, a covering sheath adapted to enclose said resistance element, a thin and coherent film of dielectric material disposed between said resistance element and said covering sheath, said resistance element formed of at least two longitudinally contiguous arcuate members connected together at one end to form a longitudinally slotted cylinder, means for connecting each section of said resistance element to a source of electric power, a body of compressible electrical insulating material filling said slotted cylinder, and means coaxial with and interior of said cylinder for compacting said insulating material to urge and maintain said resistance element in intimate contact with said covering sheath.

2. An electric heater comprising an electric resistance element, a covering sheath adapted to enclose said resistance element, a thin and coherent film of dielectric material disposed between said resistance element and said covering sheath, said resistance element formed of at least two longitudinally contiguous arcuate members connected together at one end to form a longitudinally slotted cylinder, means for connecting each section of said resistance element to a source of electric power, a finely divided refractory material adapted to fill said slotted cylinder, and means coaxial with and interior of said cylinder adapted to compact said refractory material to urge and maintain said resistance element in intimate contact with said covering sheath.

3. An electric heater comprising an electric resistance element, a covering sheath adapted to enclose said resistance element, a thin. and coherent film of dielectric material disposed between said resistance element and said covering sheath, said resistance element formed of at least two longitudinally contiguous arcuate members connected together at one end to form a longitudinally slotted cylinder, a terminal member connected to each arcuate member and projecting in an insulated manner through the opening of the endof said covering sheath to provide a connection for said resistance element to a source of electric power, a finely divided refractory material adapted to fill said slotted cylinder, and means coaxial with and interior of said cylinder adapted to compact said refractory material to urge and maintain a said resistance element in intimate contact with said covering sheath.

. 4. An electric heater comprising an electric resistance element, a covering sheath adapted to enclose said:

resistance element, a thin and coherent film of dielectric material disposed between said resistance element and said covering sheath, said resistance element formed of at least two longitudinally contiguous arcuate members connected together at one end to form a longitudinally slotted cylinder, means for connecting each section of said resistance element to a source of electric power, a refractory member adapted to fill said slotted cylinder, and means coaxial with said cylinder axis adapted to force said refractory member radially outward to urge and maintain said resistance element in intimate contact with said covering sheath.

References Cited in the file of this patent UNITED STATES PATENTS, 

1. AN ELECTRIC HEATER COMPRISING AN ELECTRIC RESISTANCE ELEMENT, A COVERING SHEATH ADAPTED TO ENCLOSE SAID RESISTANCE ELEMENT, A THIN AND COHERENT FILM OF DIELECTRIC MATERIAL DISPOSED BETWEEN SAID RESISTANCE ELEMENT AND SAID COVERING SHEATH, SAID RESISTANCE ELEMENT FORMED OF AT LEAST TWO LONGITUDINALLY CONTIGUOUS ARCUATE MEMBERS CONNECTED TOGETHER AT ONE END TO FORM A LONGITUDINALLY SLOTTED CYLINDER, MEANS FOR CONNECTING EACH SECTION OF SAID RESISTANCE ELEMENT TO A SOURCE OF ELECTRIC POWER, A BODY OF COMPRESSIBLE ELECTRICAL INSULATING MATERIAL FILLING SAID SLOTTED CYLINDER, AND MEANS COAXIAL WITH AND INTERIOR 